Crevasse Rescue & Glacier Travel Calculator
Rope spacing for a glacier team, and what a Z-drag actually delivers once friction has taken its share — which is far less than 3 to 1.
Glacier travel is taught in person, on a glacier. This page shows the arithmetic behind rope spacing and haul systems so the numbers make sense — it is not a course, and rigging a haul for the first time with someone hanging in a crevasse is not the moment to be working it out. Take a course, then practise on flat ground.
Rope spacing
Haul systems
Theory against reality
| System | Theoretical | On carabiners | On pulleys | Rope per metre |
|---|---|---|---|---|
| Direct pull (1:1) No advantage at all, but nothing to rig and nothing to go wrong. Often the right answer with enough people. | 1:1 | 1:1 | 1:1 | 1 m |
| Drop loop (2:1) Simple, needs a loop of rope reaching the casualty, and pulls in twice the rope for every metre gained. | 2:1 | 1.5:1 | 1.8:1 | 2 m |
| Z-drag (3:1) The standard crevasse-rescue system. Enough advantage for one rescuer to lift one casualty, and simple enough to rig cold and frightened. | 3:1 | 2:1 | 2.5:1 | 3 m |
| Z-drag plus drop loop (5:1) More advantage, more rope pulled per metre gained, and more to go wrong. Worth it for a heavy casualty or a rescuer working alone. | 5:1 | 2.9:1 | 3.8:1 | 5 m |
| Compound 6:1 A 3:1 pulling on a 2:1. Powerful but slow: six metres of hauling for one metre of lift, and every metre needs resetting. | 6:1 | 3.3:1 | 4.4:1 | 6 m |
| Compound 9:1 Rarely needed and rarely worth it. At this point you are moving the casualty a hand-span at a time. | 9:1 | 4.4:1 | 6.3:1 | 9 m |
Mechanical advantage is a ratio of ideal forces, and reality takes a large cut. Rope running over a carabiner loses a great deal to friction, so a 3:1 Z-drag rigged with carabiners — which is how most crevasse rescues actually get rigged, because that is what is on the harness — delivers closer to 2:1. Proper pulleys recover much of it, and the difference is precisely why they are worth carrying on a glacier and nowhere else.
What experienced teams get wrong
- Two-person teams are the hard case. There is nobody to hold the fall while somebody else builds the anchor, so both people carry the full rescue kit and both must be able to rig a haul from a hanging position.
- Tie knots in the rope between team members on a two-person team. They jam in the crevasse lip and can stop a fall before it goes far, which is worth far more than the small nuisance of hauling them back out.
- Keep the rope taut. Slack rope means a longer fall, a deeper casualty, and a harder haul — and it is the single most common thing a team gets wrong within an hour of roping up.
- Rig for rescue before you need it. A prusik already on the rope and a picket already on your pack is the difference between a five-minute rescue and an hour.
- Practise the haul on flat ground first. Everyone can describe a Z-drag; considerably fewer can rig one in gloves, in wind, with a person hanging on the other end.
How to use
- Set rope spacing for your team size before roping up.
- Keep the rope reasonably taut while travelling.
- Practise the haul system before you need it.
- Take a course — this is not learnable from a page.
Frequently asked questions
How far apart should a glacier team be?
Commonly around 10 to 15 metres between climbers on a rope of three, with more spacing for a party of two and knots often tied in the rope to help arrest a fall. Team size, crevasse size and snow conditions all change the answer, and local practice varies.
Does a Z-drag really give a 3 to 1 advantage?
Only in theory. Rope running over carabiners rather than pulleys loses a great deal to friction, and the rope cutting into the crevasse lip loses more still. Real-world figures are frequently closer to 2 to 1 or worse, which is why hauling a person out is far harder than the diagram suggests.
Why does the crevasse lip matter so much?
Because the rope cuts into the snow under load and jams, adding enormous friction and sometimes making hauling impossible until the lip is padded. Getting something under the rope at the lip is one of the first priorities in a real rescue, and it is routinely underestimated.
Is a party of two viable on a glacier?
It is done, and it is substantially harder. A single person must arrest the fall, build an anchor while holding the load, and then haul alone — every stage is more difficult than with three. Many experienced parties travel in threes on glaciated terrain for exactly this reason.
How much does this need practising?
A great deal, and in conditions resembling the real thing. Building a haul system while holding a load, in gloves, in wind, with a person's life on the rope, is nothing like doing it on the ground in good weather. Skills that are not practised regularly do not survive the situation.
Can I learn crevasse rescue from a webpage?
No, and it would be irresponsible to suggest otherwise. This is a reference for someone who has been trained, to check spacing and to think about the friction figures. Glacier travel requires proper instruction, and nothing here is a substitute for it.
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